PGSE and NOE NMR evidence for higher order aggregation in some cationic ruthenium complexes in both protic and aprotic solvents

PGSE and NOE NMR measurements were carried out for complexes [Ru(eta(6)-cymene)((2-R-C6H4)N=C(Me)-C(Me)=N(2-R-C6H4))Cl]X (X=BF4 or BPh4) in both protic and aprotic solvents with a relative permettivity (epsilon(r)) ranging from 2.27 (benzene-d(6)) to 46.45 (dimethyl sulfoxide-d(6)). PGSE and NOE results indicate that complexes have a tendency to aggregate even in medium-polarity solvents such as ethanol (epsilon(r) = 24.55) and methanol (epsilon(r) = 32.66). In addition, the aggregation process is favored by a decrease of epsilon(r) and, unexpectedly, by protic solvents. NOE measurement investigations, interpreted with the help of theoretical calculations and confirmed by X-ray single crystal studies, suggest different aggregation processes for the two counteranions: two cationic moieties approach each other when X = BF4 while the anion bridges two cationic moieties when X = BPh4.